An alkenyl aromatic compound such as a styrenic compound is a class of important industrial chemicals. For example, styrene is a starting material for resins, plastics, rubbers, and chemical intermediates. Tert-butylstyrene is useful as comonomer for preparing copolymers, as curing agent for fiber-reinforced plastics, or in improving the moldability of plastics.
It is generally known that these commercially important styrenic compounds are prepared from their corresponding precursors by thermal or catalytic dehydrogenation with steam or oxygen. The processes of dehydrogenation require expensive and sometimes complicated catalysts. Furthermore, the yield and selectivity are generally very low partly because, especially in the case of alkyl-substituted aromatic compound, the dehydrogenation can occur at carbon atoms other than the benzylic carbons. The longer the alkyl substituents, the more severe this problem becomes. Other problems include the use of very expensive starting materials, polymerization of the olefins-containing product mixtures at elevated temperatures, and extreme difficulty in separation of the desired products from undesired products, unreacted reactants and catalysts.
An oxygenated sulfur-containing compound is useful in a variety of industrial applications. For example, sulfolane can be used in pesticidal compositions, intermediates in the production of other organic chemicals, selective solvents to separate aromatic compounds from petroleum fractions, and selective solvents in alkylation of olefins.
Sulfolane-type compounds are generally prepared by catalytic hydrogenation of their corresponding sulfolene compounds. The sulfolene compounds are prepared by the reaction of a conjugated diene such as, for example, 1,3-butadiene, and sulfur dioxide at elevated temperatures.
However, the sulfolene compounds thus-produced are generally unstable and tend to decompose at mildly elevated temperatures into an unsaturated organic compound and sulfur dioxide. Furthermore, when the sulfolene compounds are used to prepare the corresponding sulfolane compounds by catalytic hydrogenation, the initiation of hydrogenation reaction may also increase the temperature enough to result in some decomposition of the sulfolene. Some of these decomposed products polymerize and the resulting polymer coats the hydrogenation catalyst significantly reducing its activity. Moreover, unreacted sulfur dioxide and the sulfur dioxide obtained from decomposition of sulfolene compounds also interfere with the subsequent catalytic hydrogenation. These sulfur dioxides must be removed or substantially reduced.
Another example of oxygenated sulfur-containing compound is bis(4,4'-chlorophenyl) sulfone that can be used as monomer for producing polymers or copolymers of aromatic sulfones. An inexpensive and easy process for producing this sulfur-containing compound has not yet been developed.
Therefore, there is an ever present need to develop more effective methods of producing an alkenyl aromatic compound such as a styrenic compound with concurrent production of an oxygenated sulfur-containing compound.